The present invention relates generally to integrated circuit chip package technology, and more particularly to a QFP exposed pad package having exposed leads on the bottom of the package body thereof, and a method of creating such exposed leads in a cost-effective manner.
Integrated circuit dies are conventionally enclosed in plastic packages that provide protection from hostile environments and enable electrical interconnection between the integrated circuit die and an underlying substrate such as a printed circuit board (PCB). The elements of such a package include a metal leadframe, an integrated circuit die, bonding material to attach the integrated circuit die to the leadframe, bond wires which electrically connect pads on the integrated circuit die to individual leads of the leadframe, and a hard plastic encapsulant material which covers the other components and forms the exterior of the package.
The leadframe is the central supporting structure of such a package. A portion of the leadframe is internal to the package, i.e., completely surrounded by the plastic encapsulant. Portions of the leads of the leadframe extend externally from the package or are partially exposed within the encapsulant material for use in electrically connecting the package to another component. In certain semiconductor packages, a portion of the die pad of the leadframe also remains exposed within the exterior of the package for use as a heat sink.
One type of semiconductor package commonly known in the electronics field is referred to as a quad flat pack (QFP) package. A typical QFP package comprises a thin, generally square package body defining four peripheral sides of substantially equal length. Protruding from each of the four peripheral sides of the package body are a plurality of leads which each have a generally gull-wing configuration. Portions of the leads are internal to the package body, and are electrically connected to respective ones of the pads or terminals of a semiconductor die also encapsulated within the package body. The semiconductor die is itself mounted to a die pad of the QFP package leadframe. In certain types of QFP packages referred to as QFP exposed pad packages, one surface of the die pad is exposed within the bottom surface of the package body.
There is a current need in the electronics industry for a QFP exposed pad package which includes leads which are exposed within the bottom surface of the package body and are included as an addition to those protruding from the sides of the package body. The present invention provides such a QPF exposed pad package wherein leads exposed within the bottom surface of the package body are provided through the use of standard, low-cost leadframe design techniques. The exposed leads of the present invention are created through utilizing a standard leadframe with additional lead features that are isolated subsequent to a mold process through the use of a partial saw method. These, as well as other features and attributes of the present invention, will be discussed in more detail below.